The present invention relates to material handling vehicles. More particularly, the invention relates to load centering devices and methods for a material handling vehicle.
Material handling vehicles are commonly found in warehouses, factories, shipping yards, and, generally, wherever pallets, large packages, or loads of goods are required to be transported from place to place. Material handling vehicles typically include load bearing forks for lifting packages or pallets for transporting, an electric drive motor for propelling the truck, a steering control mechanism, and a brake.
To improve productivity and reduce certain costs, material handling vehicles have been designed to include sensing features that allow them to be an automatic guided vehicle (AGV). An AGV may be programmed to store travel routes and include a control system which is integrated with the drive, steering, and braking systems for the vehicle. Among other reasons, sensing or locating features may be included in an AGV to detect the presence of an object to be lifted, as well as its position and orientation.
When a material handling vehicle transporting a load or object is in motion, an operator can monitor the position of the load to avoid obstacles or other objects. In AGV applications, however, an unknown position of the load requires an extended width of an object detection field to include the maximum amount the load could shift to either side of the center of the forks. Devices are available which clamp the end of a pallet closest to the operator, providing a known position of the pallet on the clamped end. These devices are manually actuated by the operator and secure the pallet on one end.
An AGV's object detection system must stop the vehicle before contact with an object. As a result, the object detection field must be wide enough to cover the vehicle and the load. Most AGVs do not change their trajectory to compensate for inexactly placed loads, however. In another situation, AGVs are used in a semi-autonomous mode where an operator performs the loading operation, and then the vehicle can perform a given task. In both cases, the vehicle does not qualify how well the pallet is loaded or its location on the forks.
From a perfectly centered position, typical pallets can shift about 4 inches to either side and still be successfully loaded. This uncertainty of knowing where the load sits on the forks results in the object detection field being wider than it needs to be. This increases the frequency of nuisance stops, or false alarms, and in other cases the additional object detection field width may prevent the vehicle from operating in potential applications. Traditional pallet clamps that only fix the pallet's location at one end do not solve the problem of securing the pallet in a known location because the far end of the pallet is free to shift laterally in a skewed fashion.
Additionally, automated systems can only accommodate variability within a specified tolerance. When one automated system interfaces with another, each has the potential to add a small amount of variability to the operation. This is added on top of any variability the system was passed from an upstream process. These tolerances accumulate (tolerance stacking) and can cause out-of-specification placement at a pickup and drop off station.
Therefore, it is an object of the invention to provide an industrial material handling vehicle that overcomes the aforementioned problems.